The invention relates to vibration exciters, more particularly for use in applying bending wave energy to panel-form structures to form loudspeakers, such as, but not limited to, the kind described in WO97/09842 and counterpart U.S. application Ser. No. 08/707,012, U.S. Pat. No. 6,332,029 filed Sep. 3, 1996.
WO97/09859 teaches the direct connection of a voice coil of an electrodynamic vibration exciter to a bending-wave panel using adhesive means, and a range of adhesives may be used to achieve such bonding. Three frequently used types are; cyanoacrylates (so-called Super Glue), two-part epoxies and doubled-sided adhesive pads. These all exhibit limitations including:
1. in production, wet adhesives are difficult to apply, particularly to castellated exciters;
2. the fumes emitted by cyanoacrylates during cure are a health hazard, which require extraction systems in production;
3. blooming of cyanoacrylates promotes crystallisation of ferrofluids;
4. gap-filling adhesives, such as two-part epoxies, require relatively large bond-line thicknesses to achieve maximum bond strength;
5. double-sided adhesive pads add (often unwanted) compliance at the exciter-panel interface, and
6. the exciter needs to be grounded if a double-sided adhesive pad is used with a castellated exciter coupler in view of the limited bond strength due to small bond area.
It is an object of the invention to avoid or at least mitigate such problems.
From one aspect, the invention is a method of making a loudspeaker comprising attaching a vibration exciter to a bending-wave panel by bringing the vibration exciter and the panel into contact over an area, and applying ultrasound energy to the contact area.
The attachment may be by ultrasonic welding.
The vibration exciter may have a thermoplastic component, and the bending-wave panel may have a thermoplastic component, and the respective thermoplastic components may be welded together.
The vibration exciter may be electrodynamic and its thermoplastic component may be a mounting foot attached to a voice coil. The mounting foot may be formed with a mounting face having at least one sharp projection in which the ultrasonic energy is concentrated during welding.
The method may comprise engaging the foot and pressing the foot into contact with the panel during application of the ultrasound energy.
The bending-wave panel thermoplastic component may be a face skin on the panel.
From another aspect the method may comprise arranging a thermally responsive adhesive to be present at the contact area and between the panel and the exciter and applying ultrasound energy to the adhesive to actuate the adhesive to bond the exciter and panel together.
The adhesive may be applied to the contact area in the form of a film.
The ultrasound energy may be applied to a face of the panel opposite to that to which the vibration exciter is attached.